This invention relates to the field of modifying the responses of plant cells to external signals, such as environmental changes, and developmental cues. More specifically, this invention provides isolated polynucleotides encoding polypeptides that are integrally located in plant cell membranes and that mediate cellular signaling processes.
Plants progress through set developmental programs throughout the course of their lifetimes. This is particularly evident in embryogenesis and floral development. There are a variety of signal molecules produced by certain cells in the plant to which other cells, particularly in the meristematic regions, are poised to respond. These signal molecules trigger distinct sets of developmental programs at specific times that lead to the formation of, for example, flowers or cotyledons. In addition to the programmed developmental pathways, plants are exposed to a variety of environmental stimuli such as changes in temperature and amount of sunlight, availability of water, wounding from mechanical injury and attack by pathogens. Environmental factors, such as exposure to light, heat, cold, drought, etc., activate the expression of genes and synthesis of proteins and other compounds essential for an appropriate response to the environmental signal and thereby, the healthy development of the plant. These responses, like the developmental pathways, are mediated by signal molecules.
To respond to these signal molecules, plant cells produce surface receptor proteins that serve as sensors, regulators and/or transducers of cell signals. The intracellular transduction of a signal is often transmitted via a phosphorylation cascade of molecules that culminates in the transcription of genes to elicit the appropriate cellular response either for normal development or against environmental challenge.
One major class of receptor proteins is the single-transmembrane family, of which there are several subclasses. These proteins are characterized by three domains: an extracellular signal molecule (or ligand) recognition/binding domain, a single cell membrane-spanning domain and an intracellular signal transduction domain which is usually a protein kinase. Many, but not all, plant single transmembrane proteins belong to the subclass known as receptor-like kinases (RLKs). The intracellular kinase domains of plant RLKs are all serine/threonine protein kinases, while the extracellular domains of RLKs are of different types. One type of RLK is characterized by the presence of the extracellular S-domain, originally described in self-incompatibility-locus glycoproteins that inhibit self-pollination. The S-domain is recognized by an array of ten cysteine residues in combination with other conserved residues. Another class of RLKs has an extracellular domain distinguished by leucine rich repeats (LRR) that are involved in protein-protein interactions. Binding of ligands to the extracellular domain is followed by receptor dimerization, autophosphorylation and the activation of a series of intracellular proteins which serve to transduce the signal to the nucleus. The structure of plant RLKs is very similar to receptors found in cell signaling pathways in animal systems.
One example of a plant RLK is the Xa21 gene, which confers resistance to the plant pathogen Xanthomonas oryzae pv. oryzae race 6. This gene was cloned using genetic means comparing Xanthomonas-sensitive and resistant strains of rice (Song et al. Science 270:1804-1806, 1995), and has been subsequently shown to confer resistance to Xanthomonas in Arabidopsis. The 1025 amino acid protein shows a number of features with similarity to known protein domains including a NH2-terminal 23 amino acid residue signal peptide, indicating that the protein is directed to the plasma membrane. Amino acids 81 to 634 contain 23 imperfect copies of a 24-amino acid LRR. Amino acids 651 to 676 encode a 26-amino acid hydrophobic segment that is likely to form a membrane-spanning domain. The C-terminal amino acids contain a putative intracellular serine threonine kinase domain carrying 11 subdomains with all 15 invariant amino acids that are typical of protein kinases. Subdomains VI and VIII are indicative of serine-threonine phosphorylation specificity. Xa21 has strong similarities to other RLKs, such as the Arabidopsis receptor-like kinase proteins RLK5 and TMK1, showing conservation of both the LRR and protein kinase domains. It is not yet known to what protein Xa21 transduces its pathogen recognition signal.
Another kind of membrane receptor molecules expressed by plant cells is histidine kinases (HKs). HKs have been known for some time in bacterial signal transduction systems, where they form one half of a two-component signaling system. The bacterial HK serves as a sensor molecule for extracellular signals, such as changes in osmoticum, nutrients and toxins. The HK autophosphorylates on a histidine residue in response to ligand binding. This phosphohistidine donates its phosphate group to an aspartate residue of the second member of the two component system, known as the response regulator (RR). The phosphorylated RR then binds DNA in a sequence-specific manner, serving to directly activate specific genes which code for proteins that mediate the response to the extracellular stimulus.
Like bacteria, plant cells have a two-component signaling system which consists of a sensor element HK and a RR. The two components may be separate molecules or may exist as a hybrid molecule (hereinafter referred to as hybrid HK/RR proteins). The HK proteins are distinguished by well-conserved amino acid motifs that occur in a specific order. From the amino terminus, the conserved regions are identified as the H, N, G1, F and G2 boxes. These motifs are usually found within a 200-250 amino acid span of the protein. The G1, F and G2 boxes are thought to be involved in nucleotide binding. As in bacteria, upon receiving the extracellular signal, the HK is autophosphorylated on the histidine residue contained in the H box. The phosphate group is subsequently transferred to the RR. All HKs are believed to phosphorylate a RR, as an obligate part of signal transduction. RRs are characterized by the absolute conservation of an aspartate which is phosphorylated by the phosphohistidine of the HK, and a conserved lysine residue. Unlike bacteria, RRs in plants have not been shown to bind DNA directly. Rather, all the plant RR""s characterized to date appear to transduce the signal into protein kinase cascades, which eventually phosphorylate and either activate or inactivate transcription factors, and thereby gene expression.
The ethylene receptor (ETR1; Chang et al. Science 262:539-544) is the best known two-component signaling system in plants. Ethylene is a well known signal molecule that is involved in the regulation of plant development as well as the coordination of fertilization, senescence, skoto/photomorphogenesis and responses to pathogens and mechanical injury. The ethylene receptor is a hybrid HK/RR protein. The signal is transduced through the protein CTR1, which is a Raf-like protein kinase. CTR1 is a negative regulator of downstream steps in the signaling pathway. While the details of this pathway remain unclear, it appears that the HK is constitutively active in the absence of ethylene, thereby constantly phosphorylating CTR1, which in turn represses other genes in the ethylene response pathway. Binding of ethylene to ETR1 inhibits the HK function of the receptor, resulting in the inhibition of the negative regulator CTR1, thereby allowing the activation of downstream proteins in the ethylene signal transduction cascade. This culminates in activation of ethylene response genes.
Recently, two RR genes, IBC6 and IBC7, which are induced in response to the plant growth regulator cytokinin, have been cloned from Arabidopsis thaliana and characterized (Brandstatter and Kieber, The Plant Cell 10:1009-1019, 1998). It is likely that IBC6 and IBC7 are involved in the transduction of the cytokinin signal in plants. This is particularly interesting in light of the fact that a gene encoding the hybrid HK/RR protein CKI1 (Kakimoto, Science 274:982-985, 1996) causes cytokinin-like effects when it is ectopically expressed in transgenic plants. Thus it appears likely that a two-component HK/RR system is involved in cytokinin signal transduction. Cytokinin is known to regulate plant growth and development, including such physiological events as nutrient metabolism, expansion and senescence of leaves, and lateral branching.
While polynucleotides encoding proteins involved in plant cell signaling have been isolated for certain species of plants, genes encoding many such proteins have not yet been identified in a wide range of plant species. Thus, there remains a need in the art for materials which may be usefully employed in the modification of cell signaling in plants.
Briefly, the present invention provides polynucleotides isolated from eucalyptus and pine which encode polypeptides involved in cell signaling, together with methods for the use of such polynucleotides and polypeptides. Such polypeptides function as sensor-regulators or receptor kinases. The isolated polynucleotides and polypeptides may be usefully employed in the modification of plant cell responses either during the growth and development of a plant, or under conditions of stress resulting from pathogens or environmental factors.
In a first aspect, the present invention provides isolated and purified polynucleotides obtainable from eucalyptus and pine which encode RLKs, HKs, RRs or hybrid HK/RR proteins. In one embodiment, the isolated polynucleotides comprise a DNA sequence selected from the group consisting of: (a) sequences recited in SEQ ID NO: 1-67; (b) complements of the sequences recited in SEQ ID NO: 1-67; (c) reverse complements of the sequences recited in SEQ ID NO: 1-67; (d) reverse sequences of the sequences recited in SEQ ID NO: 1-67; and (e) sequences having either 40%, 60%, 75% or 90% identical nucleotides, as defined herein, to a sequence of (a)-(d).
In a further aspect, isolated polypeptides encoded by an inventive DNA sequence are provided. In one embodiment, such polypeptides comprise an amino acid sequence selected from the group consisting of SEQ ID NO: 68-130.
In another aspect, the invention provides DNA constructs comprising a polynucleotide of the present invention, either alone, in combination with one or more other polynucleotides disclosed herein, or in combination with one or more known DNA sequences, together with transgenic cells comprising such constructs.
In a related aspect, the present invention provides DNA constructs comprising, in the 5xe2x80x2-3xe2x80x2 direction, a gene promoter sequence; an open reading frame coding for at least a functional portion of a polypeptide encoded by an inventive polynucleotide or a variant thereof; and a gene termination sequence. The open reading frame may be orientated in either a sense or antisense direction. DNA constructs comprising an untranslated, or non-coding, region of a gene coding for a cell membrane polypeptide encoded by the above polynucleotides or a nucleotide sequence complementary to a non-coding region, together with a gene promoter sequence and a gene termination sequence, are also provided. Preferably, the gene promoter and termination sequences are functional in a host plant. Most preferably, the gene promoter and termination sequences are those of the original genes but others generally used in the art, such as the Cauliflower Mosaic Virus (CaMV) promoter, with or without enhancers such as the Kozak sequence or Omega enhancer, and Agrobacterium tumefaciens nopaline synthase terminator may be usefully employed in the present invention. Tissue-specific promoters may be employed in order to target expression to one or more desired tissues. The DNA construct may further include a marker for the identification of transformed cells.
In a further aspect, transgenic cells, preferably plant cells, comprising the DNA constructs of the present invention are provided, together with organisms, preferably plants, comprising such transgenic cells, and fruit and seeds of such plants.
In yet another aspect, methods for modifying cell signaling in a target organism, such as a plant, are provided, such methods including stably incorporating into the genome of the plant a DNA construct of the present invention. In a preferred embodiment, the target plant is a woody plant, preferably selected from the group consisting of eucalyptus and pine species, most preferably from the group consisting of Eucalyptus grandis and Pinus radiata. In a related aspect, a method for producing a target organism, such as a plant, having modified cell signaling is provided, the method comprising transforming a plant cell with a DNA construct of the present invention to provide a transgenic cell and cultivating the transgenic cell under conditions conducive to regeneration and mature plant growth.
In yet a further aspect, the present invention provides methods for modifying the activity of a polypeptide in a target organism, such as a plant, comprising stably incorporating into the genome of the plant a DNA construct of the present invention. In a preferred embodiment, the target plant is a woody plant, preferably selected from the group consisting of eucalyptus and pine species, most preferably from the group consisting of Eucalyptus grandis and Pinus radiata. 
The above-mentioned and additional features of the present invention and the manner of obtaining them will become apparent, and the invention will be best understood by reference to the following more detailed description. All references disclosed herein are hereby incorporated by reference in their entirety as if each was incorporated individually.
The present invention provides isolated and purified polynucleotides that encode proteins involved in plant cell signaling. As discussed above, cell signaling is known to play a critical role in the growth and development of plants, and in cellular responses to external stimuli, such as environmental factors and disease pathogens. Transformation of plants with polynucleotides that encode proteins involved in cell signaling may thus be employed to modify properties such as cell proliferation, differentiation, elongation and survival; resistance to disease; and nutrient metabolism.
For example, the HK ETR1 is known to be involved in ethylene signal transduction. Modulation of ETR1 expression will thus lead to a modification of physiological properties regulated by ethylene, such as fruit ripening, and senescence of leaves and flowers. Modulation of the expression of this protein in transgenic plants may therefore be employed to prolong the useful life of cut flowers by delaying senescence. Additionally, modulation of the expression of ETR1 could be used to selectively enhance the senescence of reproductive organs, resulting in engineered sterile plants.
The HK protein CKI1 has been implicated in cytokinin signal transduction. Its over expression is known to result in cytokinin-like effects in mutant plants. Cytokinin has been shown to play critical roles in lateral branching, leaf expansion, cell division, nutrient distribution, and delaying senescence, among other physiological phenomena. Therefore, modulation of the expression of CKI1 may result in, for example, the delay of senescence in selected cell types or organs. This would result in prolonged shelf life for fruits and vegetables between harvest and consumption. Alternatively, modulation of CKI1 expression may be used to decrease branching frequency in forest tree species, resulting in long stretches of valuable knot-free clear wood for use in solid timber furniture and veneers.
Using the methods and materials of the present invention, the amount of a specific plant cell polypeptide may be increased or reduced by incorporating additional copies of genes encoding the polypeptide into the genome of a target organism, such as a plant. Similarly, an increase or decrease in the amount of the polypeptide may be obtained by transforming the target organism with antisense copies of such genes.
In one embodiment, the present invention provides isolated polynucleotides encoding, or partially encoding, plant polypeptides that are involved in cell signaling, the polynucleotides being derived from eucalyptus and pine. Specifically, the present invention provides isolated polynucleotides encoding RLKs from Eucalyptus grandis (SEQ ID NO: 2, 8, 9, 11, 15, 18, 19, 21-25, 33, 34 and 38) and Pinus radiata (SEQ ID NO: 1, 3-7, 10, 12-14, 16, 17, 20, 26-32, 35-37, 39-41), and isolated polynucleotides encoding at least one member of a two-component signaling system (HKs, RRs or hybrid HK/RR proteins) from Eucalyptus grandis (SEQ ID NO: 42, 48-52, 55-58 and 67) and Pinus radiata (SEQ ID NO: 43-47, 53, 54 and 59-66). Complements of such isolated polynucleotides, reverse complements of such isolated polynucleotides and reverse sequences of such isolated polynucleotides are also provided, together with variants of such sequences, as defined below.
In another embodiment, the present invention provides isolated polypeptides encoded by the DNA sequences of SEQ ID NO: 1-67. In specific embodiments, such isolated polypeptides include an amino acid sequence of SEQ ID NO: 68-130. The present invention also encompasses DNA sequences that differ from the disclosed sequences but which, due to the degeneracy of the genetic code, encode a polypeptide which is the same as that encoded by a DNA sequence disclosed herein.
The term xe2x80x9cpolynucleotide(s),xe2x80x9d as used herein, means a single or double-stranded polymer of deoxyribonucleotide or ribonucleotide bases and includes DNA and corresponding RNA molecules, including HnRNA and mRNA molecules, both sense and anti-sense strands, and comprehends cDNA, genomic DNA and recombinant DNA, as well as wholly or partially synthesized polynucleotides. An HnRNA molecule contains introns and corresponds to a DNA molecule in a generally one-to-one manner. An mRNA molecule corresponds to an HnRNA and DNA molecule from which the introns have been excised. A polynucleotide may consist of an entire gene, or any portion thereof. Operable anti-sense polynucleotides may comprise a fragment of the corresponding polynucleotide, and the definition of xe2x80x9cpolynucleotidexe2x80x9d therefore includes all such operable anti-sense fragments. Anti-sense polynucleotides and techniques involving anti-sense polynucleotides are well known in the art and are described, for example, in Robinson-Benion et al. (1995), Antisense techniques, Methods in Enzymol. 254(23): 363-375; and Kawasaki et al. (1996), Artific. Organs 20 (8): 836-848.
The term xe2x80x9cpolypeptidexe2x80x9d, as used herein, encompasses amino acid chains of any length including full length proteins, wherein amino acid residues are linked by covalent peptide bonds. Polypeptides of the present invention may be purified natural products, or may be produced partially or wholly using recombinant or synthetic techniques.
All of the polynucleotides and polypeptides described herein are isolated and purified, as those terms are commonly used in the art.
The definition of the terms xe2x80x9ccomplementxe2x80x9d, xe2x80x9creverse complementxe2x80x9d and xe2x80x9creverse sequencexe2x80x9d, as used herein, is best illustrated by the following example. For the sequence 5xe2x80x2 AGGACC 3xe2x80x2, the complement, reverse complement and reverse sequence are as follows:
As used herein, the term xe2x80x9cvariantxe2x80x9d covers any sequence which has at least about 40%, more preferably at least about 60%, more preferably yet at least about 75% and most preferably at least about 90% identical residues (either nucleotides or amino acids) to a sequence of the present invention. The percentage of identical residues is determined by aligning the two sequences to be compared, determining the number of identical residues in the aligned portion, dividing that number by the total length of the inventive, or queried, sequence and multiplying the result by 100.
Polynucleotide or polypeptide sequences may be aligned, and percentage of identical nucleotides in a specified region may be determined against another sequence, using computer algorithms that are publicly available. Two exemplary algorithms for aligning and identifying the similarity of polynucleotide sequences are the BLASTN and FASTA algorithms. The similarity of polypeptide sequences may be examined using the BLASTP algorithm. Both the BLASTN and BLASTP software are available on the NCBI anonymous FTP server (ftp://ncbi.nlm.nih.gov) under/blast/executables/. The BLASTN algorithm version 2.0.4 [Feb. 24, 1998], set to the default parameters described in the documentation and distributed with the algorithm, is preferred for use in the determination of variants according to the present invention. The use of the BLAST family of algorithms, including BLASTN and BLASTP, is described at NCBI""s website at URL http://www.ncbi.nlm.nih.gov/BLAST/newblast.html and in the publication of Altschul, Stephen F., et al. (1997), xe2x80x9cGapped BLAST and PSI-BLAST: a new generation of protein database search programsxe2x80x9d, Nucleic Acids Res. 25:3389-3402. The computer algorithm FASTA is available on the Internet at the ftp site ftp://ftp.virginia.edu/pub/fasta/. Version 2.0u4, February 1996, set to the default parameters described in the documentation and distributed with the algorithm, is preferred for use in the determination of variants according to the present invention. The use of the FASTA algorithm is described in W. R. Pearson and D. J. Lipman, xe2x80x9cImproved Tools for Biological Sequence Analysis,xe2x80x9d Proc. Natl. Acad. Sci. USA 85:2444-2448 (1988) and W. R. Pearson, xe2x80x9cRapid and Sensitive Sequence Comparison with FASTP and FASTA,xe2x80x9d Methods in Enzymology 183:63-98 (1990).
The following running parameters are preferred for determination of alignments and similarities using BLASTN that contribute to E values (as discussed below) and percentage identity: Unix running command: blastall -p blastn -d embldb -e 10 -G 1 -E 1 -r 2 -v 50 -b 50 -i queryseq -o results; and parameter default values:
-p Program Name [String]
-d Database [String]
-e Expectation value (E) [Real]
-G Cost to open a gap (zero invokes default behavior) [Integer]
-E Cost to extend a gap (zero invokes default behavior) [Integer]
-r Reward for a nucleotide match (blastn only) [Integer]
-v Number of one-line descriptions (V) [Integer]
-b Number of alignments to show (B) [Integer]
-i Query File [File In]
-o BLAST report Output File [File Out] Optional
For BLASTP the following running parameters are preferred: blastall -p blastp -d swissprotdb -e 10 -G 1 -E 1 -v 50 -b 50 -i queryseq -o results
-p Program Name [String]
-d Database [String]
-e Expectation value (E) [Real]
-G Cost to open a gap (zero invokes default behavior) [Integer]
-E Cost to extend a gap (zero invokes default behavior) [Integer]
-v Number of one-line descriptions (v) [Integer]
-b Number of alignments to show (b) [Integer]
-I Query File [File In]
-o BLAST report Output File [File Out] Optional
The xe2x80x9chitsxe2x80x9d to one or more database sequences by a queried sequence produced by BLASTN, BLASTP, FASTA, or a similar algorithm, align and identify similar portions of sequences. The hits are arranged in order of the degree of similarity and the length of sequence overlap. Hits to a database sequence generally represent an overlap over only a fraction of the sequence length of the queried sequence.
The BLASTN and FASTA algorithms also produce xe2x80x9cExpectxe2x80x9d or E values for alignments. The E value indicates the number of hits one can xe2x80x9cexpectxe2x80x9d to see over a certain number of contiguous sequences by chance when searching a database of a certain size. The Expect value is used as a significance threshold for determining whether the hit to a database, such as the preferred EMBL database, indicates true similarity. For example, an E value of 0.1 assigned to a hit is interpreted as meaning that in a database of the size of the EMBL database, one might expect to see 0.1 matches over the aligned portion of the sequence with a similar score simply by chance. By this criterion, the aligned and matched portions of the sequences then have a 90% probability of being the same. For sequences having an E value of 0.01 or less over aligned and matched portions, the probability of finding a match by chance in the EMBL database is 1% or less using the BLASTN or FASTA algorithm.
According to one embodiment, xe2x80x9cvariantxe2x80x9d polynucleotides, with reference to each of the polynucleotides of the present invention, preferably comprise sequences having the same number or fewer nucleic acids than each of the polynucleotides of the present invention and producing an E value of 0.01 or less when compared to the polynucleotide of the present invention. That is, a variant polynucleotide is any sequence that has at least a 99% probability of being the same as the polynucleotide of the present invention, measured as having an E value of 0.01 or less using the BLASTN or FASTA algorithms set at the parameters discussed above.
Variant polynucleotide sequences will generally hybridize to the recited polynucleotide sequence under stringent conditions. As used herein, xe2x80x9cstringent conditionsxe2x80x9d refers to prewashing in a solution of 6xc3x97SSC, 0.2% SDS; hybridizing at 65xc2x0 C., 6xc3x97SSC, 0.2% SDS overnight; followed by two washes of 30 minutes each in 1xc3x97SSC, 0.1% SDS at 65xc2x0 C. and two washes of 30 minutes each in 0.2xc3x97SSC, 0.1% SDS at 65xc2x0 C.
As used herein, the term xe2x80x9cx-mer,xe2x80x9d with reference to a specific value of xe2x80x9cx,xe2x80x9d refers to a polynucleotide comprising at least a specified number (xe2x80x9cxxe2x80x9d) of contiguous residues of any of the polynucleotides identified as SEQ ID NO: 1-67. The value of x may be from about 20 to about 600, depending upon the specific sequence.
Polynucleotides of the present invention comprehend polynucleotides comprising at least a specified number of contiguous residues (x-mers) of any of the polynucleotides identified as SEQ ID NO: 1-67 or their variants. According to preferred embodiments, the value of x is preferably at least 20, more preferably at least 40, more preferably yet at least 60, and most preferably at least 80. Thus, polynucleotides of the present invention include polynucleotides comprising a 20-mer, a 40-mer, a 60-mer, an 80-mer, a 100-mer, a 120-mer, a 150-mer, a 180-mer, a 220-mer a 250-mer, or a 300-mer, 400-mer, 500-mer or 600-mer of a polynucleotide identified as SEQ ID NO: 1-67 or a variant of one of the polynucleotides identified as SEQ ID NO: 1-67.
The inventive polynucleotides may be isolated by high throughput sequencing of cDNA libraries prepared from Eucalyptus grandis and Pinus radiata as described below in Examples 1 and 2. Alternatively, oligonucleotide probes based on the sequences provided in SEQ ID NO: 1-67 can be synthesized and used to identify positive clones in either cDNA or genomic DNA libraries from Eucalyptus grandis and Pinus radiata by means of hybridization or PCR techniques. Probes can be shorter than the sequences provided herein but should be at least about 10, preferably at least about 15 and most preferably at least about 20 nucleotides in length. Hybridization and PCR techniques suitable for use with such oligonucleotide probes are well known in the art, and include those taught by Sambrook et al., Ibid. Positive clones may be analyzed by restriction enzyme digestion, DNA sequencing or the like.
In addition, the DNA sequences of the present invention may be generated by synthetic means using techniques well known in the art. Equipment for automated synthesis of oligonucleotides is commercially available from suppliers such as Perkin Elmer/Applied Biosystems Division (Foster City, Calif.) and may be operated according to the manufacturer""s instructions.
In one embodiment, the DNA constructs of the present invention include an open reading frame coding for at least a functional portion of a polypeptide encoded by a polynucleotide of the present invention or a variant thereof. As used herein, the xe2x80x9cfunctional portionxe2x80x9d of a polypeptide is that portion which contains the binding site or the catalytic signal transduction site of the protein. The functional portion can be determined by targeted mutagenesis and screening of modified protein products with protocols well known in the art. Normally, the functional portion is 10-20 amino acids in length, but can be shorter or longer. The active site may be made up of separate portions present on one or more polypeptide chains and will generally exhibit high substrate specificity. The term xe2x80x9cpolypeptide encoded by a polynucleotidexe2x80x9d as used herein, includes polypeptides encoded by a nucleotide sequence which includes the partial isolated DNA sequences of the present invention.
The open reading frame is inserted in the DNA construct in a sense or antisense orientation, such that transformation of a target plant with the DNA construct will lead to a change in the amount of polypeptide compared to the wild-type plant. Transformation with a DNA construct comprising an open reading frame in a sense orientation will generally result in over-expression of the selected gene, while transformation with a DNA construct comprising an open reading frame in an antisense orientation will generally result in reduced expression of the selected gene. A population of plants transformed with a DNA construct comprising an open reading frame of the present invention in either a sense or antisense orientation may be screened for increased or reduced expression of the gene in question using techniques well known to those of skill in the art, and plants having the desired phenotypes may thus be isolated.
Alternatively, expression of a gene involved in plant cell signaling may be inhibited by inserting a portion of an open reading frame of the present invention, in either sense or antisense orientation, in the DNA construct. Such portions need not be full-length but preferably comprise at least 25 and more preferably at least 50 residues of an inventive DNA sequence. A longer portion or even the full length DNA corresponding to the complete open reading frame may be employed. The portion of the open reading frame does not need to be precisely the same as the endogenous sequence, provided that there is sufficient sequence similarity to achieve inhibition of the target gene. Thus a sequence derived from one species may be used to inhibit expression of a gene in a different species.
In a second embodiment, the inventive DNA constructs comprise a DNA sequence including an untranslated region of a gene coding for a polypeptide encoded by a polynucleotide of the present invention, or a DNA sequence complementary to such untranslated region. Examples of untranslated regions which may be usefully employed in such constructs include introns and 5xe2x80x2-untranslated leader sequences. Transformation of a target plant with such a DNA construct may lead to a reduction in the amount of the polypeptide expressed in the plant by the process of cosuppression, in a manner similar to that discussed, for example, by Napoli et al. (Plant Cell 2:279-290, 1990) and de Carvalho Niebel et al. (Plant Cell 7:347-358, 1995).
Alternatively, regulation of polypeptide expression can be achieved by inserting appropriate sequences or subsequences (e.g. DNA or RNA) in ribozyme constructs (McIntyre C L, Manners J M, Transgenic Res., 5(4): 257-262, 1996). Ribozymes are synthetic RNA molecules that comprise a hybridizing region complementary to two regions, each of which comprises at least 5 contiguous nucleotides of a mRNA molecule encoded by one of the inventive polynucleotides. Ribozymes possess highly specific endonuclease activity, which autocatalytically cleaves the mRNA.
The DNA constructs of the present invention further comprise a gene promoter sequence and a gene termination sequence, operably linked to the DNA sequence to be transcribed, which control expression of the gene. The gene promoter sequence is generally positioned at the 5xe2x80x2 end of the DNA sequence to be transcribed, and is employed to initiate transcription of the DNA sequence. Gene promoter sequences are generally found in the 5xe2x80x2 non-coding region of a gene but they may exist downstream of the open reading frame, in introns (Luehrsen, K. R., Mol. Gen. Genet. 225:81-93, 1991) or in the coding region, as for example in a plant defense gene (Douglas et al. EMBO J. 10:1767-1775, 1991).
A variety of gene promoter sequences which may be usefully employed in the DNA constructs of the present invention are well known in the art. The gene promoter sequence, and also the gene termination sequence, may be endogenous to the target plant host or may be exogenous, provided the promoter is functional in the target host. For example, the promoter and termination sequences may be from other plant species, plant viruses, bacterial plasmids and the like. Preferably, gene promoter and termination sequences are from the inventive sequences themselves.
Factors influencing the choice of promoter include the desired tissue specificity of the construct, and the timing of transcription and translation. For example, constitutive promoters, such as the Cauliflower Mosaic Virus 35S (CaMV 35S) promoter, will affect the activity of the enzyme in all parts of the plant. Use of a tissue specific promoter will result in production of the desired sense or antisense RNA only in the tissue of interest. With DNA constructs employing inducible gene promoter sequences, the rate of RNA polymerase binding and initiation can be modulated by external stimuli, such as light, heat, anaerobic stress, alteration in nutrient conditions and the like. Temporally regulated promoters can be employed to effect modulation of the rate of RNA polymerase binding and initiation at a specific time during development of a transformed cell. Preferably, the original promoters from the gene in question, or promoters from a specific tissue-targeted gene in the organism to be transformed, such as eucalyptus or pine, are used. Other examples of gene promoters which may be usefully employed in the present invention include mannopine synthase (mas), octopine synthase (ocs) and those reviewed by Chua et al. (Science, 244:174-181, 1989).
The gene termination sequence, which is located 3xe2x80x2 to the DNA sequence to be transcribed, may come from the same gene as the gene promoter sequence or may be from a different gene. Many gene termination sequences known in the art may be usefully employed in the present invention, such as the 3xe2x80x2 end of the Agrobacterium tumefaciens nopaline synthase gene. In one embodiment, terminator sequences are those from the original enzyme gene or from the target species to be transformed.
The DNA constructs of the present invention may also contain a selection marker that is effective in plant cells, to allow for the detection of transformed cells containing the inventive construct. Such markers, which are well known in the art, typically confer resistance to one or more toxins. One example of such a marker is the NPTII gene whose expression results in resistance to kanamycin or hygromycin, antibiotics which are usually toxic to plant cells at a moderate concentration (Rogers et al. in Methods for Plant Molecular Biology, A. Weissbach and H. Weissbach, eds., Academic Press Inc., San Diego, Calif. (1988)). Transformed cells can thus be identified by their ability to grow in media containing the antibiotic in question. Alternatively, the presence of the desired construct in transformed cells can be determined by means of other techniques well known in the art, such as Southern and Western blots.
Techniques for operatively linking the components of the inventive DNA constructs are well known in the art and include the use of synthetic linkers containing one or more restriction endonuclease sites as described, for example, by Sambrook et al., (Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratories, Cold Spring Harbor, N.Y., 1989). The DNA construct of the present invention may be linked to a vector having at least one replication system, for example E. coli, whereby after each manipulation, the resulting construct can be cloned and sequenced and the correctness of the manipulation determined.
The DNA constructs of the present invention may be used to transform a variety of target organisms, including plants, both monocotyledonous angiosperms(e.g. grasses, corn, grains, oat, wheat and barley), dicotyledonous angiosperms (e.g. Arabidopsis, tobacco, legumes, alfalfa, oaks, eucalyptus, maple), and Gymnosperms (e.g. Scots pine (Aronen, Finnish Forest Res. Papers, vol. 595, 1996), white spruce (Ellis et al., Biotechnology 11:94-92, 1993), and larch (Huang et al., In Vitro Cell 27:201-207, 1991)). In a preferred embodiment, the inventive DNA constructs are employed to transform woody plants, herein defined as a perennial tree or shrub whose stem increases in diameter each year by the addition of woody tissue. Preferably the target plant is selected from the group consisting of eucalyptus and pine species, most preferably from the group consisting of Eucalyptus grandis and Pinus radiata. Other species which may be usefully transformed with the DNA constructs of the present invention include, but are not limited to: pines such as Pinus banksiana, Pinus brutia, Pinus caribaea, Pinus clausa, Pinus contorta, Pinus coulteri, Pinus echinata, Pinus eldarica, Pinus ellioti, Pinus jeffreyi, Pinus lambertiana, Pinus monticola, Pinus nigra, Pinus palustrus, Pinus pinaster, Pinus ponderosa, Pinus resinosa, Pinus rigida, Pinus serotina, Pinus strobus, Pinus sylvestris, Pinus taeda, Pinus virginiana; other gymnosperms, such as Abies amabilis, Abies balsamea, Abies concolor, Abies grandis, Abies lasiocarpa, Abies magnifica, Abies procera, Chamaecyparis lawsoniona, Chamaecyparis nootkatensis, Chamaecyparis thyoides, Huniperus virginiana, Larix decidua, Larix laricina, Larix leptolepis, Larix occidentalis, Larix siberica, Libocedrus decurrens, Picea abies, Picea engelmanni, Picea glauca, Picea mariana, Picea pungens, Picea rubens, Picea sitchensis, Pseudotsuga menziesii, Sequoia gigantea, Sequoia sempervirens, Taxodium distichum, Tsuga canadensis, Tsuga heterophylla, Tsuga mertensiana, Thuja occidentalis, Thuja plicata; Eucalypts, such as Eucalyptus alba, Eucalyptus bancroftii, Eucalyptus botyroides, Eucalyptus bridgesiana, Eucalyptus calophylla, Eucalyptus camaldulensis, Eucalyptus citriodora, Eucalyptus cladocalyx, Eucalyptus coccifera, Eucalyptus curtisii, Eucalyptus dalrympleana, Eucalyptus deglupta, Eucalyptus delagatensis, Eucalyptus diversicolor, Eucalyptus dunnii, Eucalyptus ficifolia, Eucalyptus globulus, Eucalyptus gomphocephala, Eucalyptus gunnii, Eucalyptus henryi, Eucalyptus laevopinea, Eucalyptus macarthurii, Eucalyptus macrorhyncha, Eucalyptus maculata, Eucalyptus marginata, Eucalyptus megacarpa, Eucalyptus melliodora, Eucalyptus nicholii, Eucalyptus nitens, Eucalyptus nova-anglica, Eucalyptus obliqua, Eucalyptus obtusiflora, Eucalyptus oreades, Eucalyptus pauciflora, Eucalyptus polybractea, Eucalyptus regnans, Eucalyptus resinifera, Eucalyptus robusta, Eucalyptus rudis, Eucalyptus saligna, Eucalyptus sideroxylon, Eucalyptus stuartiana, Eucalyptus tereticornis, Eucalyptus torelliana, Eucalyptus urnigera, Eucalyptus urophylla, Eucalyptus viminalis, Eucalyptus viridis, Eucalyptus wandoo and Eucalyptus youmanni; and hybrids between any of the above species.
Techniques for stably incorporating DNA constructs into the genome of target plants are well known in the art and include Agrobacterium tumefaciens mediated introduction, electroporation, protoplast fusion, injection into reproductive organs, injection into immature embryos, high velocity projectile introduction and the like. The choice of technique will depend upon the target plant to be transformed. For example, dicotyledonous plants and certain monocots and gymnosperms may be transformed by Agrobacterium Ti plasmid technology, as described, for example by Bevan (Nucl. Acid Res. 12:8711-8721, 1984). Targets for the introduction of the DNA constructs of the present invention include tissues, such as leaf tissue, dissociated cells, protoplasts, seeds, embryos, meristematic regions; cotyledons, hypocotyls, and the like. One method for transforming eucalyptus and pine is a biolistic method using pollen (see, for example, Aronen 1996, Finish Forest Res. Papers vol. 595, 53pp) or easily regenerable embryonic tissues.
Once the cells are transformed, cells having the inventive DNA construct incorporated in their genome may be selected by means of a marker, such as the kanamycin resistance marker discussed above. Transgenic cells may then be cultured in an appropriate medium to regenerate whole plants, using techniques well known in the art. In the case of protoplasts, the cell wall is allowed to reform under appropriate osmotic conditions. In the case of seeds or embryos, an appropriate germination or callus initiation medium is employed. For explants, an appropriate regeneration medium is used. Regeneration of plants is well established for many species. For a review of regeneration of forest trees see Dunstan et al., Somatic embryogenesis in woody plants. In: Thorpe, T. A. ed., 1995: In Vitro Embryogenesis of Plants. Vol. 20 in Current Plant Science and Biotechnology in Agriculture, Chapter 12, pp. 471-540. Specific protocols for the regeneration of spruce are discussed by Roberts et al., (Somatic Embryogenesis of Spruce. In: Synseed. Applications of synthetic seed to crop improvement. Redenbaugh, K., ed. CRC Press, Chapter 23, pp. 427-449, 1993). The resulting transformed plants may be reproduced sexually or asexually, using methods well known in the art, to give successive generations of transgenic plants.
As discussed above, the production of RNA in target plant cells can be controlled by choice of the promoter sequence. A target plant may be transformed with more than one DNA construct of the present invention, thereby modulating the activity of more than one polypeptide, affecting polypeptide activity in more than one tissue, or affecting polypeptide activity at more than one expression time. Similarly, a DNA construct may be assembled containing more than one open reading frame coding for a polypeptide encoded by a polynucleotide of the present invention or more than one untranslated region of a gene coding for such a polypeptide. The polynucleotides of the present invention may also be employed in combination with other known sequences encoding polypeptides involved in plant cell signaling.
The isolated polynucleotides of the present invention may also be employed as probes to isolate DNA sequences encoding polypeptides involved in cell signaling from other plant species, using techniques well known to those of skill in the art, such as routinely used DNA hybridization and PCR techniques.
The inventive polynucleotides, polypeptides expressed by such polynucleotides and antibodies to such polypeptides may be used to screen for molecules that interact with such polynucleotides and/or polypeptides and that thereby modulate cell signaling. Techniques for performing such assays are well known in the art. Similarly, the polynucleotides and corresponding expressed polypeptides of the present invention may be employed in studies designed to elucidate the mechanism of cell signaling pathways.